It's known from the art that child safety seat with a five point harness and two tongue buckle will be fixed to the base or the frame structure of the car seat by bringing the two tongue buckle in alignment and engaging the tongues with the corresponding mother piece of the buckle to lock the buckle.
It is the purpose of the two tongue buckle as known in the art for several years to avoid misuse by accidently pressing the release button of the buckle. To ensure that only older children are able to open and release the buckle, at certain minimum amount of manual force needs to be applied to the opening button to press the button in a certain direction in order to release the two tongue buckle.
It is also a known problem in the art to fasten a child in a child safety seat with a predetermined force in order to ensure optimal restrained conditions in a child safety seat. A known solution to this problem is to have an adjuster strap situated underneath the two tongue buckle whereby the adjuster strap is connected to the harness in order to tighten the harness once the child is positioned properly in the child safety seat. In many known child safety seats the webbing runs through several openings and is guided through pulleys and reverse rollers to guarantee that the entire webbing of the five point harness can be tightened by a single adjuster strap.
One disadvantage of having the webbing run through various reverse rollers and pulleys is that the friction between the webbing and the individual guiding means causes the user to apply a very high manual force to tighten the webbing. It is not unusual that the user applies a substantial amount of physical force to tighten the webbing and is also successful in pulling the adjuster strap tightly but still experiences loose parts of the webbing, especially above the shoulder where the shoulder pads are situated.
Since a substantial feature of the child safety seat is to ensure that a child is restrained in an accident by means of the shoulder harness it is a significant disadvantage to have additional slack in the lap belt which can feed through to the shoulder belt in the event of either an accident or child movement which again may lead to slack in the harness